The present invention applies to engine control systems and particularly to throttle control systems for electronic fuel control systems.
Many vehicle throttle control systems now use electrical circuitry to deliver an electrical signal from the accelerator, e.g. an accelerator pedal or hand control lever, to an electronic fuel control system. For example, a voltage signal provided to the electronic fuel control system corresponds to accelerator pedal or hand control position. When an "in-range" voltage level arrives at the electronic fuel control system, the electronic fuel control system responds by injecting a corresponding volume of fuel into the engine fuel system.
In some applications, a control device failure can result in an invalid in-range throttle condition, i.e. an unintended in-range voltage level. Under such condition, even though the accelerator control device is at an idle position, the electronic fuel control system receives an erroneous throttle control signal and undesirably injects fuel into the engine fuel system. Loss of engine throttle control, and possibly unintended vehicle acceleration, can result. To avoid such error conditions, a separate idle validation switch has been added to the accelerator control device as backup protection against such a failure. Typically, this switch provides a single pole double throw function wherein one side of the switch delivers a logic signal corresponding to valid idle operation only and the other side validates throttle operation. The switch mounts to the accelerator control device in such a way that actuation of the accelerator control changes the switch position from its idle validation position to its throttle validation position. The electronic fuel control system ignores the throttle control signal until it receives a throttle validation signal by way of the switch.
Accordingly, if an erroneous in-range throttle signal arrives at the electronic fuel control system, unintended fuel delivery is avoided because the electronic fuel control system has not yet received a throttle validation signal.
The idle validation switch attaches to the accelerator pedal or hand control as a separate component. The switch mounts to the accelerator control device in such manner to provide the switching according to pedal or hand control lever position. It is necessary to adjust or calibrate the point at which the switching occurs to coincide with a specified throttle signal level, i.e. a point of transition between idle and throttle operation. This insures that the switch is in the idle valid mode when the driver releases the accelerator control device, and that the engine will have a smooth idle to power transition when the driver applies the throttle. Switch transition points are typically specified by the engine manufacturer. Installation of the switch can be difficult because of the sensitive calibration required to meet the engine manufacturer's specifications, and the complex test procedures needed to insure that proper switch functioning occurs. Additionally, the switch must meet stringent environmental quality standards to function reliably in typical operating environments.
These factors result in an expensive idle validation switch and, in some cases, marginal product reliability. The resulting product is also virtually impossible to service in the field without replacing the entire accelerator control assembly. Such difficult field service further adds to the overall cost of such idle validation systems.